Travelling at a hair under 9000 miles per hour, even a modest rock leaves a mark. And the 10-foot projectile that touched down in the high plains of Peru in September of 2007 did more than just scar the terrain: The 43-foot-wide crater reached into a water deposit under the town of Carancas, and the superheated meteor blasted steam laced with arsenic into the surrounding area, causing a rash of unusual illness, with symptoms ranging from nausea, vomiting and skin ailments.

The Carancas impact won't go down in history as a great distaster, or even minor one. But it is one data point in a worrying trend of minor to midsize impacts and explosions--a house-sized meteor that vaporized in a 50-kiloton explosion over rural Indonesia last year, and a one kiltoton explosion over a desolate area of the Sudan in 2008--that arrived without significant warning.

These smaller meteors, say John L. Tonry, of the Institute of Astronomy at the University of Hawaii, are "most likely" to be the cause of deadly impacts in the future--not the half-mile-wide and larger objects that NASA is currently able to track. And while these objects wouldn't result in epoch-defining impacts, they could still wreak terrible damage. A Nuclear Regulatory Commission report claimed that an object with a 50 meter diameter could kill upwards of 30,000 people if it landed in a populous area.

The size and frequency of objects like this have heretofore made tracking them nearly impossible. Tonry, however, has devised a method for discovering small to medium sized asteroids weeks in advance, and at a stunningly low cost:

This facility, entitled "Asteroid Terrestrial-impact Last Alert System" (ATLAS) would use an array of eight wide-eld, fast telescopes equipped with large detectorarrays to scan the visible sky (20,000 sq deg) twice per night. Its sky completeness gives us a better than 50% chance of detecting any 50 m asteroid approaching from a random direction, and its sensitivity provides three week's warning of 140 m objects and one week for 50 m asteroids.

The total bill? "We believe that a fully equipped telescope with focusser, filters, shutter, camera adapter and mount should cost about $50k." Sensors and operational costs would likely double the total.

The system tracks asteroids by taking a full survey of the visible sky twice a night, at a one-hour interval. The resolution of the telescape array is high enough that objects as small as 50 meters in diameter will theoretically be discernable by software at least a week in advance of impact.

A 50% chance of detection with as little as a week's warning time might not sound ideal, but it's a far sight than the detection rate we have now--effectively zero--and enough time to plan for an evacuation. In the context of the NASA budget, or the entire defense budget, the ~$1,000,000 cost is negligible.

Tonry's full proposal is viewable here. It's thorough, and I'll leave to to the vastly more qualified reviewers at NASA to decide if it has practical merit. If it does, it's an investment I imagine most governments and their citizens would be more than willing to make.

Pictured: a fragment of the Carancas meteorite courtesy of Wikimedia Commons